Nonheat-reactive resins

Substituted nonheat-reactive resins do not form a film and are not reactive by themselves, but are exceUent modifier resins for oleoresinous varnishes and alkyds. Thein high glass-transition temperature and molecular weight provide initial hardness and reduce tack oxygen-initiated cross-linking reactions take place with the unsaturated oils. 

The goal of initial phenolic resin efforts was the development of a cheap thermoplastic resin replacement for shellac. The result was the phenol/formaldehyde, nonheat-reactive resins that Baekeland referred to as novolaks. These products did not have the toughness of shellac and, therefore, never became successful substitutes. 

Phenolic resins can be divided between heat-reactive and nonheat-reactive resins and between resins made by using unsubstituted or substituted phenols. A review of the four resulting classifications follows. 

During the thirties many substituted phenols were screened for applicability in varnishes. Patents on the preparation of oil-soluble resins were issued to Honel (20) using p-tert-butylphenol and p-tert-amyIphenol and to Turkington and Butler (21) using p-tert-buty Iphenol, octylphenol, and others. Turkington and Allen (22) reported the effect of the alkyl substituent on the phenol and the Influence on resin and varnish properties. Of some 40 tested, only the acid-catalyzed, nonheat-reactive resins made with p-phenylphenol and a few para tertiary alkylated phenols gave good performance. 

The solubility of phenolic resins in different coating formulations is, however, affected by the type and chain length of substituent groups in the phenols. Depending on whether substituted or unsubstituted phenols are used, the phenolic resins can be further classified into two more groups of heat- and nonheat-reactive resins, having different applications. 

Substituted heat-reactive resins are most widely used in contact-adhesive appHcations and, to a lesser extent, in coatings (77,78) -butylphenol, cresol, and nonylphenol are most frequendy used. The alkyl group increases compatibiHty with oleoresinous varnishes and alkyds. In combination with these resins, phenoHcs reduce water sensitivity. Common appHcations include baked-on and electrical insulation varnishes, and as modifiers for baking alkyds, rosin, and ester gum systems. Substituted heat-reactive resins are not used for air-dry coatings because of theh soft, tacky nature in the uncured state substituted nonheat-reactive phenoHcs are the modifying resin of choice in this case. 

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

Raw Materials Base-Catalyzed Reactions Acid-Catalyzed Reactions Classification of Phenolic Resins Unsubstituted and Heat Reactive Unsubstituted and Nonheat Reactive Substituted and Heat Reactive Substituted and Nonheat Reactive Applications... 

These resins are less Important in coatings than their nonheat-reactive counterparts. They do find use in combination with drying oils in making electrical coil impregnation varnishes. The oils used in this type application are blown with air so that they contain enough oxygen to cross-link but are still fluid. The... 

Phenolic resins are obtained by reacting phenols (P) with formaldehyde (F) under different reaction conditions, such as in the presence of acidic or basic catalysts or at different P/F ratios. Depending upon the reaction conditions, phenolic resins are classified as novolac or resol resins (also termed nonheat- or heat-reactive resins, respectively). Resols are usually obtained when condensation is carried out in the presence of excess formaldehyde and under alkaline conditions, whereas novolacs are prepared under acidic conditions in the presence of excess phenol. The chemistry and technology of phenolic resins has recently been reviewed in the literature. ... 

Unsubstituted and nonheat-reactive phenolic resins are used to a very limited extent due to their nonfilm-forming character. These resins are generally used as hardeners with epoxy resins to produce thermoset systems with high-quality engineering plastic properties. The base-catalyzed curing produces a crosslinked polyether structure, as shown in reaction (30), which is resistant to chemicals and heat and shows good barrier properties against moisture vapour. 

---